Mucins are heavily glycosylated, high molecular weight glycoproteins with a carbohydrate content of up to 80% that are secreted by epithelial tissues. Mucins have been identified as tumor-associated antigens and have been found to be released into the circulation in large amounts by most carcinomas
(Rittenhouse et al. Lab. Med. 16: 556 (1985), Magnani et al. Cancer Res. 43: 5489 (1983), Linsley et al. Cancer Res. 46: 5444 (1986), incorporated herein by reference).
The diagnosis of colorectal cancer is currently based upon clinical findings, detection of blood in fecal samples, and a correlation with high level of certain carcinoma- associated mucin antigens in tissue, blood, or serum samples detected by the binding of certain monoclonal antibodies. Examples of monoclonal antibodies which have been reported to recognize antigens associated with gastrointestinal or colorectal cancer include CA 19-9 (Magnani, J. L. et al. supra), CCK061 (European Patent Application, EP200464) and a monoclonal antibody specific for carcinoembryonic antigen (1116NS-3d), U.S. Pat. No. 4,349,528). In vitro diagnostic methods for detecting the presence of cancer cells or other cancer cells producing small intestine mucin antigens and/or large intestine mucin antigen and monoclonal antibodies useful therein are disclosed by Linnane (PCT Publication WO 86/00414). Many other malignant conditions are also detected, in addition to colorectal carcinoma (e.g., stomach, gall bladder, malignant lymphoma and acute lymphocytic leukemia). Diagnostic tests based on each of the antigens recognized by the above antibodies fail to have a high correlation with colorectal carcinoma, particularly in its early stages, resulting in high numbers of false positive results. The only truly reliable method to date is biopsy of potentially malignant growths. Monoclonal antibodies such as CEA or CA 19- 9 are used in conjunction with other diagnostic methods or in post-therapy survey for cancer recurrance.